SECTION 2 RADIOACTIVE WASTE

Introduction

This Section describes how radioactive waste is categorised in the UK and provides some information on the type, quantity and description of the radioactive wastes included in the Scottish Government's Higher Activity Radioactive Waste Policy.

Radioactive substances are used in the nuclear and non-nuclear industries for a wide variety of reasons including generation of electricity, medical diagnosis and treatment, research and as part of industrial processes. These uses of radioactive substances results in the production of radioactive waste. Any material contaminated by or incorporating radioactivity above certain activity levels defined in legislation, and for which no further use is envisaged, is known as Radioactive Waste. In practice this radioactive waste often comprises of everyday items that have become contaminated by contact with radioactive materials, concrete and other building materials from decommissioning buildings on nuclear sites and components that have become activated in nuclear reactors.

Radioactive waste is categorised into four groups:

High Level Waste ( HLW),

Intermediate Level Waste ( ILW),

Low Level Waste ( LLW), and

Very Low Level Waste ( VLLW).

The following diagram shows the different categories of radioactive waste and how they fit into the broader descriptions of higher and lower activity waste.

The definitions of low level radioactive waste given in this document are taken from the "Policy for the Long Term Management of Solid Low Level Radioactive Waste in the United Kingdom" published in March 2007. The definitions of intermediate and high level radioactive waste are taken from Cm2919.

The definitions are those used in the United Kingdom, other countries may use different definitions.

2.01 Categories of radioactive waste

2.01.01 Radioactive waste is divided into categories according to how much radioactivity is contained in the waste and the heat that the radioactive waste produces.

Figure 1: Diagram of Waste Categories (Source Scottish Government)

High Level Waste ( HLW)

2.01.02 High Level Waste ( HLW) is radioactive waste where the temperature may rise significantly as a result of their radioactivity, so that this factor has to be taken into account in designing storage or disposal facilities.

Intermediate Level Waste ( ILW)

2.01.03 Intermediate Level Waste ( ILW) is waste with radioactivity levels exceeding the upper boundaries for Low Level Waste ( LLW) and which does not generate enough heat for heat generation to need to be taken into account in the design of storage or disposal facilities.

Low Level Waste ( LLW) and Very Low Level Waste ( VLLW)

2.01.04 Low Level Waste ( LLW) is defined as "radioactive waste having a radioactive content not exceeding four gigabecquerels per tonne ( GBq/te) of alpha or 12 GBq/te of beta/gamma activity".

2.01.05 Very Low Level Radioactive Waste ( VLLW), is a sub-category of LLW and is defined differently for low volume and high volume disposals.

"Radioactive waste which can be safely disposed of to an unspecified destination with municipal, commercial or industrial waste ("dustbin" disposal), each 0.1m 3 of waste containing less than 400 kilobecquerels (kBq) of total activity or single items containing less than 40 kBq of total activity.

2.01.07 For wastes containing carbon-14 or hydrogen-3 (tritium):

in each 0.1m 3, the activity limit is 4,000 kBq for carbon-14 and hydrogen-3 (tritium) taken together; and

for any single item, the activity limit is 400 kBq for carbon-14 and hydrogen-3 (tritium) taken together. Controls on disposal of this material, after removal from the premises where the wastes arose, are not necessary."

2.01.08 in the case of bulk disposals - High Volume VLLW:

"Radioactive waste with maximum concentrations of four megabecquerels per tonne ( MBq/te) of total activity which can be disposed of to specified landfill sites. For waste containing hydrogen-3 (tritium), the concentration limit for tritium is 40 MBq/te. Controls on disposal of this material, after removal from the premises where the wastes arose, will be necessary in a manner specified by the environmental regulators".

2.01.09 The principal difference between the definitions for high volume and low volume VLLW is the need for controls on the total volumes of VLLW in the high volume category being deposited at any particular landfill site.

2.02 Where does higher activity radioactive waste come from?

2.02.01 The majority of higher activity radioactive waste arises from the operation and decommissioning of nuclear sites in Scotland. However, some higher activity wastes may arise from activities in the non-nuclear industry as well.

2.03 Operational and Decommissioning Wastes

2.03.01 Radioactive wastes are often described as 'operational wastes' and 'decommissioning wastes'.

2.03.02 Decommissioning wastes are produced during the dismantling of nuclear facilities, and make up the bulk by volume of the higher activity waste that will be produced in Scotland. The majority of these wastes are made up of graphite, metals and concrete from reactors and will need to be managed when the reactors are dismantled.

2.03.03 Operational wastes are produced during the research or electricity generation activities that take place on nuclear sites. Examples of operational waste include laboratory consumables or fuel debris, which is produced during the management of spent fuel and comprises parts of the fuel casings.

2.04 Intermediate Level Waste

2.04.01 Intermediate Level Waste arises mainly from the reprocessing of spent fuel and from general operations and maintenance at nuclear sites, and can include metal items such as fuel cladding and reactor components, graphite from reactor cores, and sludges from the treatment of radioactive liquid effluents. Currently, ILW is packaged for disposal by mixing it with cement in highly-engineered 500 litre stainless steel drums (or for large items in higher capacity steel or concrete boxes).

2.05 Higher activity radioactive waste in Scotland

2.05.01 The following pie chart is based on data from the 2007 National Inventory and shows the proportion by volume of each higher activity radioactive waste type that is estimated to arise from Scottish nuclear sites. The data used to create this pie chart is given in 2.07 with a breakdown of waste type for each of the nuclear sites in Scotland and how the final packaged volume has been calculated.

(Please note due to rounding factors with some small numbers the total percentage comes to over 100%)

2.06 How is the Waste described?

Waste Descriptions

2.06.01 A 'waste description' is a convenient way of grouping types of wastes together which have similar physical, chemical or radionuclide properties and can be used to determine how they might be treated, stored or disposed of.

2.06.02 This process is comparable to how domestic waste can be divided into separate groups, such as paper to be recycled or garden waste to be composted. For radioactive materials this gives us a range of broad groupings which then allows for a collective method of treatment, packaging and disposal appropriate to a waste stream's specific properties.

2.06.03 The following pages describe the different types of higher activity waste produced in Scotland. The percentages given are the proportion by volume of each waste type based on information from the 2007 National Inventory.

Graphite (45%)

Graphite is a solid form of the element carbon that is used in nuclear reactors to slow down neutrons in the reactor core so that fission can take place. Fission is the process of splitting atoms to produce energy. During this process the graphite itself becomes radioactive due to bombardment with neutrons.

Activated Metals (15%)

Metal items such as structural components and fuel assembly cladding that have been used inside a reactor. These metal components become radioactive due to bombardment with neutrons.

Contaminated Metals (14%)

Metal items such as tools and pipework that have been contaminated on the surface with radioactivity. Contamination occurs when items are in contact with radioactive material, traces of which are transferred to them. This contamination is often limited to the surface of the metal items

Raffinates (8%)

Raffinates can be held in metal drums like these shown.

Raffinates are waste liquids produced during the reprocessing of nuclear fuel by the process of solvent extraction. The raffinates consist of nitric acid containing a mixture of radioactive fission and activation products left behind after the majority of the uranium and plutonium have been extracted.

Sludges (4%)

Sludges are a mixture of solid and liquid material that comprise waste products from reprocessing operations, and corrosion products from the storage of wastes

Concrete (3%)

Concrete is used in the construction of nuclear reactors and associated facilities for structural, shielding and containment purposes. It can become contaminated during the operational lifetime of the nuclear reactor. Contaminated regions of concrete are removed as waste during the decommissioning of nuclear facilities.

Desiccant (3%)

A desiccant is a substance, usually in the form of small beads, that is used to dry reactor coolant gases. Gases containing tritiated water vapour pass through the desiccant and it traps the water leaving contaminated desiccant behind. Tritiated water is water that contains the radioactive isotope tritium.

Plutonium contaminated materials (2%)

Any material that has been contaminated with the radioactive element plutonium.

These materials can be held in metal drums like these shown.

Fuel debris (2%)

Fuel debris consists of small pieces of metallic waste (magnox alloy) produced when parts of the fuel element casings are removed. There is also the possibility of small pieces of metal uranium fuel being present in the waste.

Hazardous chemicals (1%)

Hazardous chemicals, such as acids, are used in various processes associated with the operation and decommissioning of nuclear reactors and associated facilities. These hazardous chemicals become contaminated with radioactive elements during their use and need to be disposed of as radioactive waste.

Ion Exchange Resins (1%)

Ion exchange resins consist of small beads used to remove radioactivity from contaminated liquids. The radioactive ions in the liquid are absorbed onto the resin by the chemical process ion exchange. The resins retain the activity and the cleaned liquids can then be safely disposed of. When the ability of the resins to absorb more radioactive ions is exhausted they become radioactive waste.

Thorium contaminated materials (1%)

Any material that has been contaminated with the radioactive element thorium or materials that contain thorium left after the processing of thorium fuel.

Catalysts (< 0.5%)

A catalyst is a substance that is used to increase or decrease the rate of a chemical reaction. The catalysts can become contaminated during use and become radioactive waste.

Uranium contaminated materials

(< 0.5%)

Any material that has been contaminated with the radioactive element uranium.

Oils and solvents (< 0.5%)

Oils and solvents that are used in various processes associated with the operation and decommissioning of nuclear reactors that have been contaminated with radioactivity.

Sealed radioactive sources (< 0.5%)

Sealed radioactive sources consist of radioactive material in a container, which is designed to seal in the radioactive material. Sealed radioactive sources are used in many industry sectors including health, education and manufacturing. In the nuclear industry they are mainly used for the calibration of instruments. Sealed radioactive sources become radioactive waste when they are no longer needed

Other (1%)

Any higher activity radioactive waste that is not included in any of the other categories described.

2.07 How much Waste is there in Scotland?

2.07.01 The following table is based on data from the 2007 National Inventory and shows the volume in cubic metres (m 3) of each higher activity radioactive waste type that is estimated to arise from each of the nuclear sites in Scotland.

2.07.02 The table shows the total stored volume of each waste type and the packaging factor that is applied to give the total packaged volume ready for disposal. The packaging factor shows the amount that the stored volume needs to be multiplied by to give the total volume after treatment and packaging. The volume change is because material might be added or removed during treatment and to include packaging that is added following treatment. This packaging factor and the packaged volume are based on current treatment methods and may change if new treatment and packaging methods are developed.